Location: Livestock and Range Research Laboratory
Project Number: 3030-31000-018-007-I
Project Type: Interagency Reimbursable Agreement
Start Date: Jun 1, 2019
End Date: May 31, 2023
1. Determine the effect of exogenous estradiol administration on pregnancy establishment and maintenance in cows induced to ovulate with GnRH. These studies will be led by ARS investigator. 2. Characterize the physiological role of estradiol on estrogen responsive genes in the endometrium and conceptus growth and gene expression that contribute to increased pregnancy success in cattle. These studies will be led by by both ARS and non-ARS investigators.
Specific Aim 1 – Estrous cycles will be synchronized in suckled beef cows (n = 400/yr for 2 years) using the 7-d CO-Synch + CIDR protocol. Cows that fail to express estrus by 48 h post PGF (approximately 50 % of cows) will receive either saline or estradiol (E2) coincident with GnRH2. All cows (Estrual, saline and E2) will receive an in vivo produced embryo of similar stage and quality from the same flush on d 7. Blood will be collected at d -2, d 0 (GnRH2), and d 1 to measure E2 concentrations and d 7, 19, 24, and 30 for measure of P4, ISGs, and PAG. Hormones and pregnancy signals will be compared between estrual cows and non-estrual cows that receive saline or E2. Pregnancy will be evaluated by measure of ISGs and PAGs on d 19, 24, and 30, and via ultrasound on d 30 and 42. This study will be led by ARS investigator. Specific Aim 2 – Cows (n = 62) will receive the same synchronization, E2 or saline treatments, and embryos as in Specific Aim 1. Cows will be harvested and reproductive tracts collected from 16 pregnant cows per day (8 saline + 8 E2 cows) on d 20, 24, 28, and 32 of gestation. At harvest, pictures will be taken to document gross morphological differences in vascularity of the chorioallantoic membrane and cotyledonary size between treatments. The conceptus will be gently removed and the uterine horn flushed with sterile PBS. Uterine lumen flush (ULF) will be clarified and subjected to mass spectrometry to evaluate proteins, metabolites, fatty acids and prostaglandins. The embryo will be separated from extraembryonic membranes and gene expression from both tissues, as well as endometrial gene expression will be measured using deep sequencing. Tissue collection will be led by ARS investigator and gene expression profiling will be led by non-ARS investigator.